GB2027157A

GB2027157A - Recovering pipelines

Info

Publication number: GB2027157A
Application number: GB7910702A
Authority: GB
Original assignee: Saipem SpA
Current assignee: Saipem SpA
Priority date: 1978-07-28
Filing date: 1979-03-27
Publication date: 1980-02-13
Also published as: JPS6222037B2; DK144807C; FR2431951A1; IE790744L; NO150410C; JPS5522587A; DE2913335B2; NL177711C; NZ189988A; BR7903358A; GB2027157B; FR2431951B1; BE875795A; AU523174B2; NL177711B; CA1092375A; NL8501730A; IT7826236A0; US4234268A; IE47872B1

Description

1 GB 2 027 157 A 1.

SPECIFICATION Recovering a submerged pipeline

This invention relates to apparatus for inserting a recovery plug into a submerged pipeline for recovering the pipeline.

Our British Patent Application No. 7717/77 (Serial No. 1546335) discloses and claims apparatus for inserting a recovery plug into a submerged pipeline for recovering the pipeline, comprising a support having clamping means for clamping the support rigidly on a submerged pipeline to be recovered; a cutter mounted on the support in such a position as to be disposed to cut through the pipeline, when the support is clamped on the pipeline, to afford a pipeline end; a recovery plug mounted moveably and releasably on the support; drive means for moving the plug relatively to the support between a rest position and an inserted position in which, when the support is clamped on the pipeline, the plug is inserted in the 85 pipeline end; plug retaining means mounted releasably on the support; and means for moving the plug retaining means into a position in which it engages the pipeline and the plug to retain the plug in the inserted position.

The same patent application also describes and claims a method of recovering a submerged pipeline, the method comprising:

(a) lowering apparatus as just defined to the pipeline to be recovered; (b) clamping the apparatus to the pipeline using the clamping means (c) cutting through the pipeline using the cutter; (d) moving the plug from the rest position to the inserted position; (e) operating the plug retaining means to retain the plug within the pipeline; (f) releasing the plug from the support; and (g) raising the plug with the pipeline to the surface.

The apparatus described in patent application No. 7717/77 has various drawbacks. In the rest position, the plug is supported vertically and this needs a support which is high and therefore very bulky and consequently heavy. This is turn requires the use of high power lifting equipment on board the vessel on the surface, with a consequent increase in the cost of the work necessary for recovery. In addition, the large overall size considerably increases the difficulties involved in mounting it in the pipeline to be recovered, particularly in strong underwater currents. A further drawback of the apparatus described in patent application No. 7717/77 is that the clamping means comprises two pairs of jaws which are relatively close together, and they can induce a bending moment in the end part of the pipeline which can cause distortion or kinking of that end part. Further, according to the depth and conditions of the sea, the pipeline may have a reinforced concrete casing over the bitumen or plastics coating, in order to give it the necessary weight to keep it stationary on the sea bed under strong current conditions. This considerably bomplicates and prolongs the cutting operation, and also leads to easy fracture of the cutter. A further drawback of the apparatus described in patent application No. 7717/77 is that it is inflexible and is not suited to carrying out the multiplicity of different types of lifting and recovery operations. For example, the recovery plug is locked inside the pipeline to be recovered only by pinning. This pinning operation, which requires considerable time for dri ' Iling a hole in the pipeline and the one-off use of a special locking dowel provided with retaining means, is very costly; while this cost is justified in recovering large diameter heavy pipelines in bad conditions, where water in the pipeline has not been removed, the pinning operation is uneconomical when recovering pipelines of modest weight or pipelines which are empty, especially under good sea conditions. Under these conditions, it would be sufficient to simply lock the plug by means of radially mobile shoes which would not require perforating the pipe. Furthermore, with the apparatus described in patent application No. 7717/7 7, the water which may fill the pipeline can only be removed through the plug, and not in the opposite direction as is sometimes required. this is because the plug does not have a pig such as an emptying ball or cylinder because there is no effective sealing system between the plug and the pipeline which prevents losses in the pneumatic thrust necessary for driving the pig.

According to the present invention there is provided apparatus for inserting a recovery plug into a submerged pipeline for recovering the pipeline, comprising a support having clamping l 00 means for clamping the support rigidly on a submerged pipeline to be recovered; cutting means mounted on the support in such a position as to be disposed to cut through the pipeline, when the support is clamped on the pipeline, to 105 afford a pipeline end; a recovery plug disposed parallel to the length of the pipeline, when the support is clamped on the pipeline; a carriage to which the recovery plug is releasably connected and which is mounted on the support, the carriage being displaceable relatively to the support in a direction parallel to the length of the pipeline, when the support is clamped on the pipeline, and being pivotable relative to the support about a pivot axis parallel to that direction; drive means for displacing and pivoting the carriage relatively to the support to move the recovery plug from a rest position to an inserted position in which, when the support is clamped on the pipeline, the plug is inserted in the pipeline end; and plug retaining means which is operable to retain the plug axially in the inserted position.

In an embodiment of the present invention, the recovery plug in the rest position is supported above the support, and thus it is possible to provide a structure of very small overall size which is therefore easy to handle. To position the plug in front of the pipeline end, the carriage is slid outwardly from the support by a double-acting hydraulic cylinder, and is rotated through 1801 by 2 GB 2 027 157 A 2 a hydraulic motor. The plug is then inserted into the pipeline by sliding the carriage back into the support, using the same double-acting hydraulic cylinder.

The clamping means preferably comprises two pairs of hydraulically operated jaws which are mounted at a large distance apart from one another and cooperate with inclined surface seats.

With such a construction, kinking of the pipeline is avoided and the seating of the apparatus on the pipeline is facilitated.

Preferably, the cutting means comprises a part circular toothed carrier which has a recess bounded by inclined planes to facilitate seating on the pipeline. The carrier is supported for 80 rotation within a circular guide of a support member fixed to the support. A rocker is pivotally mounted on the carrier and has a hydraulic motor at each end, each motor being connected to drive a cutter. One cutter is suitable for cutting a 85 concrete casing of the pipeline, and the other is suitable for cutting a steel lining. The rocker is controlled by two double-acting hydraulic cylinders to bring one or the other of the cutters into contact with the pipeline. The part-circular toothed carrier is rotatable by two drive gears which mesh with it and are supported rotatably on opposite sides of the support member. Each drive gear is driven, through a worm, a spindle and two bevel gears, by a hydraulic motor mounted on the support member.

Thus, by operating one or the other of the two hydraulic cylinders, one of the cutters is pressed against the pipeline to cut the pipeline. The use of two separate drive gears for rotating the carrier ensures that it is rotated completely through 3600, even though it is not circumferentially continuous.

Preferably, the recovery plug comprises three separable cylindrical members. The first cylindrical 105 member is provided with a central tube, and with a transverse bore into which a locking dowel provided with retaining members can be inserted to pin the plug to the pipeline. The first member also has a locking mechanism in the form of radially mobile shoes which can be operated remotely by fluid from hydro-pneumatic accumulators incorporated in the first cylindrical member. Between the first and second members there is positive locating means. The second cylindrical member has a central channel which communicates with the central tube and has a mechanism for sealing against the pipeline by axial compression of plastics sealing rings. The sealing mechanism is operable remotely by fluid from the hydro-pneumatic accumplators passing through hydraulic lines through both the first and second cylindrical members. The third cylindrical member comprises a pig and is coupled with the second cylindrical member by a remotely releasable retaining pin. The pig is mounted on a spigot of the second cylindrical member, through which extends the central channel. The central channel opens into a thrust chamber in the pig.

Thus, the plug can be retained inside the pipeline in the most satisfactory manner for the prevailing conditions, either by using the locking dowel or by using the radially mobile shoes, or both. Water can be forced from the pipeline in the direction away from the plug by forcing gas under pressure through the aligned central passages for driving the pig, the necessary gas being supplied by storage cylinders arranged inside the first cylindrical member, or by a hose connected between the first cylindrical member and the pipelaying vessel.

In order to prevent leakage of gas into the transverse bore in the first cylindrical member, the central tube of the first cylindrical member has a loop which passes around the transverse bore and the central channel of the second cylindrical member has a corresponding loop, the two loops being aligned and mating so that they intercommunicate when the first and second cylindrical members are coupled together.

For a better understanding of the present invention and to show how it may be carried into effect, reference will now to be made, by way of example only, to the accompanying drawings, in which:

Figure 1 is a side view of apparatus for recovering a submerged pipeline clamped on to the pipeline to be recovered; Figure 2 is a sectional view taken on the line AA in Figure 11; Figure 3 is a sectional view taken on the line BB in Figure 1; and Figure 4 is a partial sectional view of the end of the pipeline with a recovery plug inserted in it.

With reference to the figures, recovery apparatus 1 is shown during recovery from the sea bed 2 of a damaged pipeline having a steel lining 3 and a concrete casing 4. In Figure 1, a damaged pipeline portion 5 is shown as being separated from the rest of the pipeline. The apparatus comprises a hollow beam 6 of square cross section and comprises two upper lugs 7 and 8 each provided with a series of holes 9. A shackle - f-1 is pivotally connected between the lugs 7 and 8 by a pin 10 which passes through one of the holes in each lug. The shackle 11 is reinforced by a plate 12 and is connected by a ring 14 in a hole 15 in the shackle 11 to a cable 13 run from a pipelaying vessel. The beam 6 is guided down to the pipeline to be recovered in a manner similar to that described in British patent application No 7717/77 by means of a guide cable 16 run from the pipelaying vessel and secured to the pipeline by a hydraulic clamp 17. A guide ring 18 runs on the cable 16 and is releasably secured by a double-acting hydraulic cylinder 19 to the end of a bracket 20 fixed to one end of the beam 6.

A beam 26 is supported in the beam 6 and can move axially by means of four pairs of free-running wheels 21, 22,23 and 24 mounted on axles 25 supported by the beam 6. The beam 26 is lightened by making holes 27 in it, and it has at one end a plate 28 the purpose of which is to cooperate with the end 29 of the beam 6 to limit the movement of the beam 26 into the beam 6.

3 GB 2 027 157 A 3 The beam 26 can be driven axially in both directions by a double-acting hydraulic cylinder 30 accommodated in the lower part of the interior of the beam 6. A piston which is slidable in the cylinder 30 is rigidly connected to the plate 28 by 70 a piston rod 3 1. The cylinder 30 can be supplied with fluid under pressure from hydro-pneumatic accumulators 32 accomodated in the beam 6, and can be remotely controlled by a pushbutton on a pushbutton control panel 33 situated on the beam 75 6. The plate 28 is fitted with a spigot 34 carrying a laterally extending carriage 35 which can pivot freely about the spigot 34 and releasably supports a recovery plug 36 disposed parallel to the beams 6 and 26. The end 37 of the carriage 35 has a dovetailed tenon 37 for insertion into a corresponding dovetailed groove in a block 38 fastened to the plug 36, the two being locked together by a pin 39 carried by the piston of a double-acting hydraulic cylinder 40 fixed to the block 38. The cylinder 40 can be supplied with fluid under pressure from hydro-pneumatic accumulators 41 (see Figure 4) accommodated in the plug 36, and can be remotely controlled by a pushbutton of another pushbutton control panel 42 situated on the plug. The carriage 35 can be rotated about the spigot 34 by a hydraulic motor 43 which is mounted on the carriage 35, and can be supplied with fluid under pressure from the accumulators 41 by way of a further pushbutton on the pushbutton control panel 42. The drive shaft of the motor 43 carries a gearwheel 44 which constantly meshes with a gear wheel 45 fixed on the spigot 34, these gear wheels being housed in a compartment in the carriage 35.

While the apparatus 1 is being lowered on the cable 13 from the pipelaying vessel on to the pipeline to be recovered, the beam 26 is fully retracted ' inside the beam 6, with the plate 28 abutting the end 29 of the beam 6; the carriage 105 is rotated upwards. In this manner, the recovery plug 36 is supported above and parallel to the beam 6, as indicated in dashed outline 36 in Figure 1; this configuration keeps the overall size of the apparatus to a minimum.

Below the beam 6 there is fixed a beam 46, lightened by holes 47. At each end of the beam 46 there is a seat 48 or 49 each having a boundary comprising inclined diverging planes 50 and 51 so (see Figure 3), which facilitate the seating of the 1 apparatus 1 on the pipeline to be recovered. A pair of arms 52 and 53 is carried on each seat 48 or 49 by means of pivots 54 and 55 respectively.

Each arm 52 and 53 has a jaw 521 and 53', and the arms are driven to clamp the apparatus to the pipeline to be recovered by a double-acting hydraulic cylinder 56 pivotally connected to the ends of the arms and supplied with fluid under pressure from the hydro-pneumatic accumulators 34, under the control of a further pushbutton on the pushbutton control panel 33.

Below the beam 6 is fixed a support block 57 which is substantially in the form of a inverted U (Figure 2), which carries cutting means 58, for cutting away the possibly damaged pipeline portion 5, and a locking device 59 for making a hole the pipeline and for inserting a locking pin provided with retainers through the hole and into a transverse bore 60 in the plug,36. This locking device 59 is supported by the block 57, between the pair of jaws supported by the seat 49 and the cutting means 58, in a position at which the transverse bore 60 of the plug 36 is located when the plug is completely inserted into the pipeline to be recovered. This occurs when the plate 28 of the beam 26 makes contact with the end 29 of the beam 6. The locking device 59 is similar to that described in the British patent application No. 7717/77, and comprises a locking dowel 61 provided with retainers and on the end of which is screwed a cutter 62 (see Figure 2). The dowel 61 is screwed to the piston of a hydraulic cylinder 63 which is rotated, together with the dowel, by a hydraulic motor 64 supported by the support block 57. The cutting means 58 comprises an externally toothed part- circular carrier 65 (see Figure 2), which has a'recess with inclined diverging edges 66 and 67 to facilitate the seating of the ring on the pipeline to be recovered. The carrier 65 is rotatably supported by an arcuate guide 68 in the support block 57, and supports at its upper central region a rocker 69, which is pivoted to the carrier 65 by a pin 70. The rocker 69 has at one end a hydraulic motor 71 driving a cutter 72 and at the other end a hydraulic motor 73 driving a cutter 74. The two motors 71 and 73 can be supplied with fluid under pressure from the hydro-pneumatic accumulators 32 under the control of a pushbutton on the pushbutton control panel 33. The two cutter s 72 and 74, which are generally of different types, one being for cutting the concrete casing 4 and the other being for cutting the lining 3, are moved in operation one after another into a working position, i.e. they are lowered and pressed against the pipeline by two_ double acting hydraulic cylinders 75 and 76 respectively, which are pivotally connected to supports 66, 67 fixed to the bottom of the toothed carrier 65 by pivots 77. The piston rods 78 and 79 of the cylinders 75 and 76 are hinged to the respective ends of the rocker 69. The toothed carrier 65 can be rotated through 3600 by two _gear wheels 80 and 81 which are in constant mesh with the toothed ring and are rotatably supported by pivots 82 on opposing sides of the support block 57. Each gearwheel is driven by a hydraulic motor 84 supported by the support block 57, through a mechanism consisting of a worm 85 which meshes with the gear wheel 80 or 81 and is carried by a spindle 86 which is connected to one end of the drive shaft of the hydraulic motor 84 by a pair of bevel gears 87. All of the members 80-87 are supported in a suitable cavity in the support block 57. Both of the double-acting hydraulic cylinders 75 and 76 and the hydraulic motor 84 are supplied with fluid under pressure from-the hydro-pneumatic accumulators 32 and are remotely controlled by corresponding pushbuttons of pushbutton control panel 33.

The plug 36 is an assembly of three separable 4 GB 2 027 157 A 4.

cylindrical members. The first of these members 65 comprises a cylindrical body 88 which fits into the pipeline to be recovered and is connected to a cylindrical body 89 which is of greater radius than the body 88, and terminates in a rounded cap 90 provided with a mechanism 91 for the automatic coupling of a lifting cable 92 for lifting the pipeline to the pipelaying vessel, this mechanism 91 being similar to that described in British patent application No. 7717/77 Serial No. 1546335.

The first cylindrical member 88, 89 of the plug 75 36 has an axially extending central tube 93 (see Figures 1 and 4) which opens at the surface of the plug, on one side of said body 89, at a discharge port 94 provided with a non-return valve. The central tube 93 is also connected to another port for a hose connected to the pipelaying vessel, through which gas can be fed into the tube for driving a pig for expelling the water in the pipeline in a direction away from the plug. The port 95 is also situated on the side of the body 89, and is provided with a non-return valve. The central tube 93 is also connected directly through a conduit provided with a non-return valve, not shown on the Figure, to a system of storage cylinders 96 housed in a chamber in the body 89, and filled with the gas for driving the pig.

The non-return valves are operated by fluid from the hydro-pneumatic accumulators 41 in the body 89, under remote control, by means of pushbuttons on the pushbutton control panel 42 situated on the side of the body 89. At the end of the body 88 of the first plug member there is the transverse bore 60 into which the locking device 59 inserts the locking pin 61. To prevent the transverse bore 60 also going through the central tube 93, thus leading to leakages, the tube 93 has an elbow or loop 97 going around the bore 60.

The cylindrical body 88 of the first plug member is also provided with a retaining mechanism in the form of radially extendable shoes. This mechanism 105 is substantially similar to that already described in our Italian patent No. 983,826 granted on 11 November 1974, and is constituted in practice by two sets of shoes 98 and 99 which can be pressed radially against the inner surface of the pipeline 3. 110 The shoes 98 and 99 are accommodated in apertures 100 and 101 provided in the body 88, and can be moved by two corresponding sets of opposed wedges 102 and 103 which cooperate with pins 104 carrying the shoes. The wedges 102 and 103 are rigid respectively with two telescopic sliders 105 and 106 which are slidable longitudinally along the central tube 93. These sliders define between them two chambers 107 and 108 which are connected by control valves, not shown in the Figure, to the hydro-pneumatic accumulators 41, these valves being controlled by pushbuttons on the pushbutton control panel 42.

Finally, the cylindrical body 88 is provided at its end with lugs 109 which are inserted into suitable guides in the second cylindrical member 110 of the plug 36 to locate the second member 110 positively relatively to the first member 88, 89 the two being coupled together in a ny manner, for example by means of a screw coupling. The second cylindrical member 110 is provided with a sealing mechanism operating by axial compression of plastic rings, this mechanism being substantially similar to that already described in out Italian patent No. 983,826. The mechanism comprises two plastics sealing rings 111 and 112 of circular cross-section, which are separated from each other by a longitudinally slidable metal ring 113 of trapezoidal cross-section. The rings 111 and 112 are compressed axially against the inclined walls of the ring 113, and, respectively, against the inclined wall 114 of a block 115 rigid, with the end of the second cylindrical member 110, and against the inclined wall 116 of a slider 117 slidable longitudinally on the body of the second cylindrical member 110, with which the slider 117 forms two chambers 118 and 119 which are connected to the hydro-pneumatic accumulators 41 by two hydraulic conduits, not shown on the figure, and provided in the second cylindrical member 110, and by a further two hydraulic conduits which are aligned with the first two, these also not being shown on the Figure but being provided in the first cylindrical member 88, 89 of the plug 36. Communication between the corresponding conduits is ensured by the location of the first and second cylindrical members. The chambers 118 and 119 are supplied with fluid under pressure under the control of pushbuttons on the pushbutton control panel 42, which operate control valves in the conduits. Said second member 110 is also provided axially with a central channel 120 which, at the end adjoining the body 88 of said first cylindrical member, is in the form of an elbow or loop 121 corresponding to the loop 97 of the central tube 93, so that when the two loops 93 and 121 are aligned and communicate, the central channel 120 constitutes an extension in the second cylindrical member 110 & the central tube 93 of the first cylindrical member 88, 89. The central channel 120 of the second cylindrical member 110 extends at its other end into a cylindrical spigot 122 projecting from the second member 110, which is inserted into a corresponding bore provided in the third cylindrical member 123 of the plug 36, and opens into a thrust chamber 124 in the third cylindrical member 123. This cylindrical member 123, which 115, acts as an emptying cylinder or pig for evacuating water from the pipeline in the direction away from the plug, is provided with plastics sealing rings 125 and 126, and is removably retained on the support block 122 by a retaining mechanism which can be disengaged remotely and consists of a retaining pin 127 which is fixed to the piston of a hydraulic double-acting cylinder 128 supported by the third cylindrical member 123. This retaining pin can be moved into and out of a corresponding hole in the spigot 122, under the control of pushbuttons on the pushbutton control panel 42 which control the supply of fluid under pressure to the cylinder 128 from the hydro-pneumatic GB 2 027 157 A 5 accumulators 41 byway of interconnected 65 conduits provided in the cylindrical members of the plug 36.

Claims

1. Apparatus for inserting a recovery plug into a 70 submerged pipeline for recovering the pipeline, comprising: a support having clamping means for clamping the support rigidly on a submerged pipeline to be recovered; cutting means mounted on the support in such a position as to be disposed 75 to cut through the pipeline, when the support is clamped on the pipeline, to afford a pipeline end; a recovery plug disposed parallel to the length of the pipeline, when the support is clamped on the pipeline; a carriage to which the recovery plug is 80 releasably connected and which is mounted on the support, the carriage being displaceable relatively to the support in a direction parallel to the length of the pipeline, when the support is clamped on the pipeline, and being pivotable relative to the support about a pivot axis parallel to that direction; drive means for displacing and pivoting the carriage relatively to the support to move the recovery plug from a rest position to an inserted position in which, when the support is clamped on the pipeline, the plug is inserted in the pipeline end; and plug retaining means which is operable to retain the plug axially in the inserted position.

9. Apparatus as claimed in any one of the preceding claims, in which the cutting means comprises two cutters having different cutting characteristics from each other.

10. Apparatus as claimed in claim 9, in which one of the cutters is suitable for cutting a concrete outer casing of the pipeline and the other is suitable for cutting a steel inner liner of the pipeline.

11. Apparatus as claimed in claim 9 or 10, in which the cutters are carried by a carrier which is rotatable within a recess in a support member to move the cutters around the pipeline when the pipeline is clamped to the support and received in the recess of the support member, the cutters being mounted at opposite end regions of a rocker which is pivotally connected to the carrier whereby each of the two cutters can be selectively brought into cutting engagement with the pipeline.

12. Apparatus as claimed in claim 11, in which the support member has divergent guide walls for receiving the pipeline.

13. Apparatus as claimed in claim 11 or 12, in which the cutters are drivable in rotation by respective hydraulic motors mounted on the rocker.

14. Apparatus as claimed in any one of claims 11 to 13, in which the rocker is pivotally movable relatively to the carrier by two double-acting 2. Apparatus as claimed in claim 1, in which the 95 hydraulic cylinders which are connected between support comprises a first beam and the carriage is disposed on a second beam which is displaceable an rollers within the first beam.

3. Apparatus as claimed in claim 2, in which the second beam is provided with a spigot atone end, 100 the carriage being mounted rotatably on the spigot.

4 Apparatus as claimed in claim 3, in which the drive means comprises a hydraulic motor mounted on the carriage, which drives in rotation a gear wheel which meshes with a further gear wheel fixed to the spigot.

5. Apparatus as claimed in any one of claims 2 to 4, in which the drive means comprises a double-acting hydraulic cylinder which is mounted 110 on the first beam and is provided with a piston having a piston rod connected to the second beam.

6. Apparatus as claimed in any one of claims 2 to 5, in which the second beam is provided with an end plate which is engageable with an end of the first beam to limit retraction of the second beam into the first beam.

7. Apparatus as claimed in any one of the preceding claims, in which the clamping means comprises two pairs of hydraulically operated jaws, each pair being positioned to clamp the pipeline against a respective seat provided on the support, each seat having diverging guide walls for the pipeline.

8. Apparatus as claimed in claim 7, in which the two pairs of jaws are disposed so that, when the support is clamped on the pipeline, they are mutually axially spaced along the pipeline.

the carrier and the rocker.

15. Apparatus as claimed in any one of claims -11 to 14, in which the carrier is rotatable relatively to the support member by a hydraulic motor mounted on the suppori block and driving the carrier through a worm and worm wheel transmission.

16. Apparatus as claimed in any one of the preceding claims, in which the recovery plug comprises three axially interconnected members, the first of which is provided with at least part of the plug retaining means, the second of which is provided with sealing means for sealing the plug within the pipeline end, and the third of which is releasable from the others and comprises a pig for passage through the pipeline to expel liquid from the pipeline.

17. Apparatus as claimed in claim 16, in which the first member has connecting means for the attachment of a cable to the plug.

18. Apparatus as claimed in claim 16 or 17, in which the retaining means comprises hydraulically actuated shoes mounted on the first member and engageable with the interior of the pipeline to retain the plug in the pipeline.

19. Apparatus as claimed in any one of claiTs 16 to 18, in which the retaining means comprises a dowel releasably mounted on the support and a bore extending transversely through the first member, the dowel being rotatable and being provided at one end with a cutter for cutting through the wall of the pipeline whereby the dowel can be inserted into the bore in the first member to retain the plug within the pipeline end, 6 GB 2 027_157 A 6 the dowel having retainers for retaining it within the bore.

20. Apparatus as claimed in any one of claims 16 to 19, in which the sealing means comprises at least one plastics sealing ringl the second member 20 having hydraulically operated means for axially compressing the ring to force it radially into sealing engagement with the interior of the pipeline. 10 21. Apparatus as claimed in any one of claims 25 16 to 20, in which the pig is releasably connected to the second member by a hydraulically operable retaining pin. 22. Apparatus as claimed in any one of claims 15 16 to 21, in which a passage extends through the 30 first and second members for the supply of compressed gas to drive the pig through the pipeline.

23. Apparatus as claimed in claim 22 when appendant to claim 19, in which the passage passes around the bore.

24. Apparatus as claimed in any one of the preceding claims, in which a guide ring is releasably connected to the support for receiving a guide cable attached to the pipeline to be recovered. W 25. Apparatus for inserting a recovery plug into a submerged pipeline substantially as described herein with reference to, and as shown in the accompanying drawings.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1980. Published by the Patent Office, 25 Southampton Buildings, London, WC2A l AY, from which copies may be obtained.